1. Field of the Invention
This invention relates in general to method and apparatus for purging a string of railway cars by introducing purge gas directly to the vapor space of each car.
2. Description of the Prior Art
In prior art, loading and unloading systems for tank car and trains, the purge gas has been introduced into the cargo near the bottom of the tank which causes it to bubble up through the cargo and also to be absorbed in the cargo. U.S. Pat. Nos. 3,897,807 and 4,304,271 assigned to the assignee of the present invention disclose such prior art systems.
Such prior art systems introduce the purge gas in the induction pipe which terminates near the bottom of the tank and, thus, the purge gas passes up through the cargo or commodity before reaching the vent space and forcing the cargo out the vent pipe at the other end of the car. Also, as the purge gas passes from the end of the first car through the vent it passes into the eduction pipe of the second car and is ejected near the bottom of the tank from the eduction pipe of the second car where it passes again up through the commodity to the vent space and so on. Such prior art systems require high pressure requirements for the purge gas since the gas must be forced up through the commodity. Also, a substantial volume of gas is absorbed in the commodity.